1. Field of the Invention
The invention relates generally to a wireless communications network, like a cellular network, and more particularly to a method and system for optimizing channel quality indicator (CQI) transmissions by mobile devices during voice-over-internet-protocol (VoIP) transmissions.
2. Description of the Related Art
A cellular network is a wireless communications system made up of a number of cells, each served by a fixed transmitter, known as a cell site or base station. Each cell site in the network typically overlaps other cell sites. The most common form of cellular network is a mobile phone (cell phone) system. The base stations are connected to cellular telephone exchanges or “switches”, which in turn connect to the public telephone network or another switch of the cellular company.
The 3rd Generation Partnership Project (3GPP) is a worldwide consortium to create a specification for a globally applicable third generation (3G) mobile phone system. 3GPP's plans are currently in development under the title Long Term Evolution (LTE). The 3GPP LTE project is to improve the Universal Mobile Telecommunications System (UMTS) terrestrial radio access mobile phone standard to cope with future requirements. Goals of 3GPP LTE include improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and better integration with other open standards. The 3GPP LTE technical specification is described in a set of reference documents including 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and Modulation (Release 8), 3GPP TS 36.211 V0.4.0 (2007-02); and 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8), 3GPP TS 36.300 V8.1.0 (2007-06). In 3GPP LTE (E-UTRA and E-UTRAN) terminology, a base station is called an “eNode-B” (eNB) and a mobile terminal or device is called a “user equipment” (UE).
In 3GPP LTE, the eNB regularly transmits a downlink reference symbol (DLRS) that is used by the UEs for channel measurement, such as signal-to-interference ratio (SINR), which may be represented by a channel quality indicator (CQI). Each UE regularly transmits CQIs back to the eNB to enable the eNB to perform resource scheduling. Resource scheduling means the eNB allocates the modulation schemes, coding rates and subcarrier frequencies to optimize the downlink and uplink transmissions for each UE.
The data transmitted over the wireless network is often categorized as either non-real-time (NRT) data or real-time (RT) data. Examples of NRT data include data transmitted during web browsing by a UE or text-messaging to a UE, while an example of RT data is voice communication between UEs. The typical manner of resource scheduling for NRT data is “dynamic” scheduling by the eNB to each UE at each transmission time interval (TTI). During dynamic scheduling, the UE regularly transmits CQIs back to the eNB.
However, in 3GPP LTE the UEs are also required to transmit and receive RT data, specifically voice data, which is considered the most important application in LTE and will be carried as voice-over-internet-protocol (VoIP) transmissions. A typical VoIP session has periodic small data packets at fixed intervals and periodic silence indication (SID) packets at fixed intervals. Unlike NRT data transmission, VoIP transmission is handled using “semi-persistent” scheduling. In contrast to dynamic scheduling, in “semi-persistent” scheduling when a UE's downlink reception is enabled, if the UE cannot find its resource allocation, a downlink transmission according to a predefined resource allocation is assumed. VoIP transmission and its associated semi-persistent method of resource allocation presents special issues regarding the transmission of CQIs by the UEs. What is needed is a method and system for optimizing CQI transmissions during VoIP sessions.